Last Night's Storm Squall Line Was Classic

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Forecast Discussion: The vertical wind shear the past few days and the moisture/instability profile has been favorable for thunderstorms over Yavapai County. Because the winds are shearing from the east-northeast with height, we had a squall line from that direction yesterday evening. The squall line had all of the classic signatures of a squall line, with a leading shelf cloud, followed by a convective line, and trailing stratiform rain. The storm also produced gusty winds and anywhere from 0.4” to 1.5” of rain across the Prescott area.

This was the weather map on Tuesday.

As a result, a flash flood warning was issued on the north side of Prescott Valley. A student of mine, Jordan Stephens, took a time lapse video of the line with his GoPro camera that is definitely worth seeing:

Tonight, the atmosphere will be a bit more stable than last night and the wind shear will be slightly weaker, but we could still see multicellular lines of thunderstorms propagating from the ENE towards the WSW.

The weather information for Wednesday night.

By tomorrow, however, westerly winds will begin to develop across the Southwest as low pressure is expected to form in the upper atmosphere along the California Coast. This low pressure will remain fairly stationary for the next week or so and will bring progressively drier air across Arizona for the next 6 days or more. Therefore, expect a decreasing chance of thunderstorms Thursday – Saturday, and only a slight chance of thunderstorms (if any storms at all) Sunday - mid week next week. Storms that form after today will slowly drift eastward or northeastward and will have little organization to them. The main threat on Thursday might be localized flooding from slow-moving thunderstorms.

C. James

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